Superabrasive compacts are utilized for a variety of applications and in a corresponding variety of mechanical systems. For example, polycrystalline diamond elements are used in drilling tools (e.g., as inserts, cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire drawing machinery, and in other mechanical systems. Such superabrasive compacts may be known in the art as inserts, buttons, machining tools, wear elements, and bearing elements are typically manufactured by forming a superabrasive layer on the end of a substrate (e.g., a sintered or cemented tungsten carbide substrate). As an example, polycrystalline diamond, or other suitable superabrasive material, such as cubic boron nitride, may be sintered onto the surface of a cemented carbide substrate under ultra-high pressure and ultra-high temperature to form a superabrasive compact, as described in greater detail below. In one specific example, polycrystalline diamond compacts (PDCs) have found utility as cutting elements in drill bits (e.g., roller cone drill bits and fixed cutter drill bits).
More particularly, a PDC may be employed as a subterranean cutting element mounted to a drill bit either by press-fitting, brazing, or otherwise locking the stud into a receptacle defined by the drill bit, or by brazing the cutting element directly into a preformed pocket, socket, or other receptacle formed in the subterranean drill bit. In one example, cutter pockets may be formed in the face of a matrix-type bit comprising tungsten carbide particles that are infiltrated or cast with a binder (e.g., a copper-based binder), as known in the art. Such subterranean drill bits are typically used for rock drilling and for other operations which require high abrasion resistance or wear resistance. Generally, a rotary drill bit may include a plurality of polycrystalline compact cutting elements affixed to the drill bit body.
A PDC is normally fabricated by placing a cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains positioned adjacent one surface of a substrate. A number of such cartridges may be typically loaded into an ultra-high pressure press. The substrates and adjacent diamond crystal layers are then sintered under ultra-high temperature and ultra-high pressure conditions. The ultra-high pressure and ultra-high temperature conditions cause the diamond crystals or grains to bond to one another to form polycrystalline diamond.
Because of different coefficients of thermal expansion and modulus of elasticity, residual stresses of varying magnitudes and developed within different regions of both the superabrasive layer and the substrate, may remain in the cutting element following cooling and release of pressure. These complex stresses may be concentrated near the superabrasive table/substrate interface. Depending upon the cutting element structure, the direction of any applied forces, and the particular location within the cutting element under consideration, the stresses may be either compressive, tensile, shear, or mixtures thereof. Residual stresses at the interface between the superabrasive table and substrate may result in failure of the cutting element upon cooling or during subsequent use under thermal stress and applied forces, especially with respect to large-diameter cutting elements. These manufacturing-induced stresses are complex and may undesirably place the superabrasive table of the cutting element into tension at locations within or upon the superabrasive table and/or substrate.
During drilling operations, cutting elements may be subjected to very high forces in various directions, and the superabrasive layer may fracture, delaminate, spall, or fail due to the combination of drilling-induced stresses as well as residual stresses much sooner than would be initiated by normal abrasive wear of the superabrasive layer. Because premature failure of the superabrasive layer at the superabrasive table/substrate interface may be augmented by the presence of high residual stresses in the cutting element, attempts have been made to provide PDC cutting elements which are resistant to premature failure. For instance, the use of a transition layer with material properties intermediate of those of the superabrasive table and substrate is known in the art. Also, a variety of conventional cutting element designs in which the superabrasive table/substrate interface is three dimensional (i.e., the superabrasive layer and/or substrate have portions which protrude into the other member) exists.
Thus, it would be advantageous to provide a superabrasive compact with enhanced resistance to stress-induced damage. In addition, subterranean drill bits or tools for forming a borehole in a subterranean formation including at least one such superabrasive compact would be beneficial.